Hemp, once a major US crop, has been banned for years because of its close association with cannabis. But several states now want to resume hemp farming, and two states voted this month in favour of legalisation of cannabis. Could change be in the air?

There's an all-American plant that weaves its way throughout the nation's history.

The sails of Columbus' ships were made from it. So was the first US flag. It was used in the paper on which the Declaration of Independence was printed.

Today, however, industrial hemp is effectively banned by the federal government, damned by association with cannabis, its intoxicating cousin.

While hemp cannot be grown in the US, it can be imported and used to manufacture paper, textiles, rope, fuel, food and plastics.

Hemp's problem is that, like marijuana, it contains tetrahydrocannabinol (THC), a psychoactive chemical, albeit in much smaller doses than its better-known relative.

While the US federal Drugs Enforcement Administration (DEA) adopts a zero-tolerance policy towards THC, hemp advocates say one would have to smoke a telegraph pole-sized joint of hemp to get high from it.

But advocates of its legal cultivation believe the winds of change are blowing.

States such as Oregon, North Dakota, Vermont, Montana and West Virginia have backed its legal cultivation.

In Congress, an unlikely coalition of lawmakers ranging from right-wing Republicans to liberal Democrats are pushing for reform.

And votes in Colorado and Washington state to legalise, regulate and tax marijuana could, supporters believe, open the door of the drug's less potent relative.

After all, within living memory, fields of hemp abounded in Kentucky and the Midwest.

Hemp crop in Fayette County, central Kentucky, 1942

"If you go back to the 1940s, the US was a very large hemp producer," says Isaac Campos, an expert on the drug trade at the University of Cincinnati. "It was more profitable than corn and soya beans."

As far back as 1607, the crop was produced in Virginia. From 1619, all planters in the colony were required by law to grow it.

Founding fathers George Washington and Thomas Jefferson both cultivated hemp on their land. The cord around the US Constitution was reputedly made from hemp.

It was seen as an important crop relatively recently, too.

During World War II, it was so crucial to the military that farmers who grew it and their sons were exempted from military service. It was celebrated in a 1942 public information film, Hemp For Victory, which has since gone on to achieve cult popularity among latter-day generations of stoners.

In 1941, that most iconic of American industrialists, Henry Ford, produced a car whose plastic frame was partially made of hemp and whose engine could be powered by hemp fuel.

Henry Ford, right, with a car made of farm products such as soy, hemp and flax

"A lot of this was written out of history," says Eric Steenstra, president of the Hemp Industries Association. "But this was a historically significant crop."

Why I want to grow hemp

Wayne Hauge, 54, who farms 2,400 acres of arable land in North Dakota, campaigns for the legalisation of industrial hemp.

I've been a farmer for over 30 years. Both of my great-grandfathers were farmers. I don't exactly fit the stereotype of a pot-smoking dude. I don't want anything to do with smoking cannabis. I've never touched the stuff.

I just think industrial hemp would be profitable to grow. It's an easy crop to cultivate - practically a weed. With all crops, you need rotation. Industrial hemp merely provides another option.

I'm 50 miles from Canada. There are people not far north of here growing hemp. It seems logical to conclude it would work down here too.

At state level industrial hemp is widely supported. But when politicians get to federal level it seems their priorities change.

Around the turn of the 20th Century, hemp faced two obstacles, however.

One was the decline of the shipping industry, which meant demand for hemp ropes and sails fell.

The other was guilt by association with a substance which became the focus of an American moral anxiety.

"In Mexico by the 1890s, marijuana was believed to cause madness and violence," says Campos. "By the 1910s that idea was quite established in the US.

"There was just so much enthusiasm among the prohibitors to ban cannabis and hemp was caught up in that."

The Marihuana (sic) Tax Act of 1937 effectively banned all varieties of the plant cannabis sativa, although farmers were temporarily exempted from this while they were encouraged to grow hemp during wartime. The Controlled Substances Act of 1970 explicitly outlawed cannabinoids.

Advocates for the crop never entirely went away, however. Because hemp requires much less irrigation, and around half as much land as cotton to produce the same amount of textile, supporters of legalisation say it is much more environmentally friendly. Hemp seed and its oil, too, are championed by health food enthusiasts.

Canada's decision in 1998 to legalise the growth of hemp under licence appears to have spurred on legislators south of the border.

Since 2005, the libertarian Texas Republican Ron Paul has introduced four bills to the House of Representatives aimed at making hemp farming lawful. The most recent of these, the Industrial Hemp Farming Act of 2011, attracted 22 co-sponsors.

In August 2012, Mr Paul's son, Kentucky Senator Rand Paul, co-sponsored a bill with Oregon Democrat Ron Wyden in the upper chamber which would exempt Hemp from the Controlled Substances Act.

Industrial hemp is grown in Europe, but China is the biggest producer

Some 17 states have passed hemp-related legislation and 10 (Colorado, Hawaii, Kentucky, Maine, Maryland, Montana, North Dakota, Oregon, Vermont and West Virginia) have approved bills to remove barriers to its production.

The obstacle remains the federal authorities. Hemp cannot be grown without a DEA permit and it remains opposed to its cultivation.

"'Hemp' is simply a term used by some to create the false impression that so-called 'hemp' is not the same as marijuana," a DEA spokesman says. "In fact, under federal law, all cannabis plants (that is, all plants of the genus cannabis) are marijuana."

Opponents of legalisation say it would be extremely difficult for the authorities to tell whether illicit varieties of cannabis sativa were being surreptitiously grown amid fields of the industrial hemp crop.

However, according to Randy Fortenbery of Washington State University, who has studied the economic viability of hemp production, the voter initiatives in Washington and Colorado may make this a moot point.

"A lot of the resistance was about not being able to tell the difference between commercial hemp and crops grown for marijuana," he says.

"But if marijuana becomes more acceptable then this isn't an issue any more."

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